The present invention generally relates to drive systems that transmit power through roller and sprockets that may mesh in a non-conjugate manner and, more particularly, to compliance apparatus for such drive systems. Even more particularly, the present invention relates to employment of such drive systems for transmitting torque to wheels of an aircraft.
It is well known that, unlike an involute-gear based drive system, a roller-based drive system may not perform with conjugate action between the driving and driven elements. In other words, a roller and sprocket interaction may result in cyclical variations of angular velocity as each roller progresses through its respective meshing. This non-conjugate meshing may be problematic in certain applications such as motorcycle drive systems, automotive engine-timing drive systems or aircraft electric taxi systems (ETS).
When a conventional gearbox is employed in a drive system that may experience non-conjugate meshing of sprockets and roller, a driven member may experience cyclical acceleration pulses during the meshing of each roller. If the driven member has a large mass, for example an aircraft wheel, these cyclical pulses may not actually materialize as acceleration of the driven member because the inertia of the driven member may be too high. In that case, the cyclical pulses may be fed back into the gearbox in the form of undesirable cyclical shocks.
In an aircraft ETS, for example, it is desirable to construct the ETS with compact and lightweight components which may be retrofitted onto existing aircraft and which may perform reliably even when exposed to varying environmental conditions that may be encountered by the aircraft at various airports. To meet these conditions, some ETS drive systems employ a roller and sprocket arrangement and torque is delivered to the wheel though a driven sprocket.
Some design challenges remain even when such roller and sprocket systems are employed. For example, the wheel rims of many commercial aircraft are designed to allow a limited amount of deflection during taxiing and turning of the aircraft. During taxiing, the load of the aircraft may cause the wheel to ovalize on each revolution. Moreover, the loads exerted on the wheel may cause deflections of the wheel rim with respect to the axle. Weight on an axle during a turn may cause flexure of the wheel rim radially or axially from a driving sprocket.
Under these conditions, a center distance between a sprocket and roller may vary with wheel deflection. Thus, even if a sprocket was uniquely designed to have conjugate action at a particular center distance, the wheel deflection may vary the center distance enough to offset the benefits of the unique sprocket design.
As can be seen, there is a need for a roller-based drive system that will deliver power with non-cyclical angular velocity even when a center distance between a driving element and a driven element may vary. More particularly there is a need for such a system which may be incorporated on an aircraft ETS.